From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([2001:4830:134:3::10]:42963)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <c-d.hailfinger.devel.2006@gmx.net>)
	id 1bntMb-00075b-92
	for qemu-devel@nongnu.org; Sat, 24 Sep 2016 16:15:58 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <c-d.hailfinger.devel.2006@gmx.net>)
	id 1bntMX-000143-1E
	for qemu-devel@nongnu.org; Sat, 24 Sep 2016 16:15:56 -0400
References: <57E5752C.3080407@virtuozzo.com>
	<a3d525e9-a66e-d086-55a4-5def3824964d@redhat.com>
	<20160923212126.vo3hvb4hxojjh7s4@grep.be>
	<57E66C60.8040102@virtuozzo.com>
	<FD5348CE-88CA-4833-AB84-90D04058A9AF@alex.org.uk>
	<57E6ACDD.7080205@virtuozzo.com>
	<D47EBA1A-3256-40C2-A394-6A849F1B4B1D@alex.org.uk>
	<57E6B423.6010007@virtuozzo.com> <57E6B8CF.6040406@virtuozzo.com>
From: Carl-Daniel Hailfinger <c-d.hailfinger.devel.2006@gmx.net>
Message-ID: <57E6DEA0.7050002@gmx.net>
Date: Sat, 24 Sep 2016 22:14:24 +0200
MIME-Version: 1.0
In-Reply-To: <57E6B8CF.6040406@virtuozzo.com>
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 7bit
Subject: Re: [Qemu-devel] [Nbd] write_zeroes/trim on the whole disk
List-Id: <qemu-devel.nongnu.org>
List-Unsubscribe: <https://lists.nongnu.org/mailman/options/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.nongnu.org/archive/html/qemu-devel/>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <https://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>, Alex Bligh <alex@alex.org.uk>
Cc: "nbd-general@lists.sourceforge.net" <nbd-general@lists.sourceforge.net>, Kevin Wolf <kwolf@redhat.com>, qemu block <qemu-block@nongnu.org>, "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>, Paolo Bonzini <pbonzini@redhat.com>, "Stefan stefanha@redhat. com" <stefanha@redhat.com>, "Denis V. Lunev" <den@openvz.org>, Wouter Verhelst <w@uter.be>

On 24.09.2016 19:33, Vladimir Sementsov-Ogievskiy wrote:
> On 24.09.2016 20:13, Vladimir Sementsov-Ogievskiy wrote:
>> I agree that requests larger than disk size are ugly.. But splitting
>> request brings me again to idea of having separate command or flag
>> for clearing the whole disk without that dance. Server may report
>> availability of this/flag command only if target driver supports fast
>> write_zeroes (qcow2 in our case). 
> Also, such flag may be used to satisfy all needs:
>
> flag BIG_REQUEST is set and length = 0    ->    request on the whole 
> disk, offset must be 0
> flag BIG_REQUEST is set and length > 0    ->    request on 
> (offset*block_size, length*block_size), length*block_size must be <= 
> disk_size

What happens if length*block_size<=disk_size, but
offset*block_size+length*block_size>disk_size? Wraparound?

Regards,
Carl-Daniel